Users of irons have demanded that irons, first, deal with a bulk of clothes at one time and, second, be lightweight for ease of ironing. The U.S. Pat. No. 5,042,179 discloses an iron having two large heaters for controlling steam production depending on ironing cycles, which intends to meet the first demand of the users. The disclosed iron can thus supply steam appropriately to respective ironing cycles, and also deal with a bulk of clothes at one time.
However, the disclosed iron has a pressurizing steam generator for supplying steam smoothly, so that the iron is heavy. This iron thus places a heavy load on the users. Further, since this iron requires a large amount of heat, the iron must always be powered, and this model is thus far from being a cordless type iron. In these years, cordless irons have become widely used because they can make ironing easier. A cordless iron must accumulate a large amount of heat therein and be lightweight at the same time. The iron disclosed by the U.S. Pat. No. 5,042,179 has some heat accumulation effect because steam is stored by pressurizing; however, this structure results in a heavy body.
A conventional cordless iron is described hereinafter with reference to FIG. 17. The iron 1 comprises (a) a base 3 including a vaporizing chamber 2, (b) a heater 4 for heating the base 3, (c) a water tank 5 disposed above base 3 for pooling water, and (d) a valve 7 for opening/closing a channel for supplying the water in tank 5 to a watercourse 6.
Valve 7 comprises the following elements:
a steam button 8 mounted above water tank 5 so that the button 8 can move up and down (i.e., such that one push moves the button down, and another push moves the button up); PA1 an open/close pole 9 which travels up and down together with the steam button 8 and which has a latch function; and PA1 a spring 10 for urging both pole 9 and button 8 in the upward direction. PA1 (a) a first base to be directly heated; PA1 (b) a second base including a soleplate; and PA1 (c) a thermal resistance layer between the first and second bases.
A lower end of pole 9 forms a hemisphere and engages in an upper end of watercourse 6 so that the lower end of pole 9 can block water from flowing into the watercourse 6 from the water tank 5.
The watercourse 6 is disposed above vaporizing chamber 2, and the water in water tank 5 is dripped into vaporizing chamber 2 through a drip hole 11. The soleplate of base 3 is provided with steam vents 12 from which the steam from vaporizing chamber 2 spouts.
A thermistor type temperature sensor 13 for sensing a temperature of base 3 is placed on base 3. This temperature sensor 13 and a control circuit 14 control the heating of heater 4, so that the iron is controlled to maintain an appropriate temperature.
An operation of the structure discussed above is described hereinafter. First, a user turns on a switch to provide power to heater 4. The heat of heater 4 transfers to base 3 and heats base 3. After that, temperature sensor 13 senses that base 3 is heated up to a given temperature, and then control circuit 14 cuts off the heating of heater 4.
Since base 3 dissipates some heat, the temperature of the iron lowers after a while whether the user operates the iron or leaves it. Temperature sensor 13 senses the lowered temperature, and again supplies power to heater 4 to start heating. The range of temperature fall is predetermined, and a range of ca. 10.degree. C. is generally employed.
An operation of using the steam is described hereinafter. When the iron is heated up to the given temperature, the user pushes steam button 8 against spring 10, which releases a latch mechanism and moves pole 9 upward, and watercourse 6 is then opened. The water in tank 5 drips into vaporizing chamber 2 through drip hole 11 due to gravity. The dripped water dissipates the heat from base 3 and vaporizes into steam, then spouts from steam vents 12.
In this conventional structure, however, the base temperature lowers so soon that it is hard to smooth wrinkles of a bulk of clothes, particularly in the case of a cordless iron. This structure also sustains a spray of steam for only a short period. Therefore, when a bulk of clothes must be ironed, or a so called power-shot demanding a lot of steam is required, the base temperature lowers so soon that the user must halt the ironing to allow the heater to heat up again. This lowers the operational efficiency.
In the cordless iron, the sustainable period of spraying steam is determined by an amount of heat accumulated. In other words, the accumulated heat amount Q depends on a specific heat "c", a mass "W", and a temperature "T" of the base; Q=cWT.
The accumulated heat amount increases at the greater values of these three factors. Regarding the specific heat "c", no practical material featuring a lightweight and a higher specific heat can replace aluminum, which is presently employed as a base material.
Regarding the mass "W", there is some limit to increasing the mass (weight) of the base, because the users must hold the iron during the operation. It is thus impractical to increase the weight of the iron. In general, the iron weighs 1.1 kg including 600 g of the base. This is the upper limit to practical use.
Regarding the temperature "T", since the base 3 and the soleplate are unitarily formed, the temperature of base 3 must be adjusted to be appropriate for respective materials of clothes. The temperature of base 3 cannot be further raised from the present condition, in order to protect the clothes. The "high mode" of the present model is ca. 220.degree. C., and this is the upper limit.
Another conventional type of iron is shown in FIG. 18, where an upper base 15 and a lower base 16 are used instead of the base 3; however, the heat from the upper base 15 instantly transfers to the lower base 16, and this structure thus produces the same effect as the base 3 unitarily formed with the soleplate.